It is known to produce ophthalmic lenses, in particular contact lenses such as soft contact lenses, in an automated production process with reusable molds. Such automated production of hard and soft contact lenses is very efficient and allows the mass production also of contact lenses, which are worn only once and then replaced with new contact lenses. In order to ensure a high and constant quality level of the contact lenses, the produced contact lenses are optically inspected.
However, ophthalmic lenses, in particular soft contact lenses, are difficult to inspect using mechanical means for holding them during inspection. It is known to hold the contact lenses immersed in a liquid, for example water, in a cuvette for the purpose of optical inspection. The cuvette comprises a receptacle which may be made of a light-transmitting material either entirely or at least along the optical axis of the optical inspection system, and an inspection window arranged in an opening of the receptacle. To create the conditions required for such optical inspection of contact lenses, it is on one hand necessary to ensure that the liquid, the inspection window and the walls of the receptacle which are arranged in the optical path during inspection, are clean. On the other hand, there must not be a free boundary surface of the liquid which may adversely affect the image, and no air bubbles must be present between the inspection window and the liquid. Accordingly, the underside (lower surface) of the inspection window is immersed in the liquid contained within the receptacle.
For inspection, the cuvette containing the contact lens to be inspected is placed in the optical path of the optical inspection system in a manner such that an image of the contact lens may be recorded by a camera, which may comprise a suitable image-resolving sensor.
In a known cuvette, the receptacle and the inspection window are fixedly pre-assembled to form a one-piece cell, with the inspection window closing an upper opening of the receptacle. In order to be able to fill the cell with liquid and to insert and remove the contact lens from the cell, the one-piece cell is provided with a lateral extension forming a handling channel, which is arranged inclined with regard to a longitudinal axis of the cell by an angle of about 45°. A bottom of the one-piece cell is shaped in such a manner, that the cell may be tilted from a stable handling position in which the cell can be filled with liquid and in which the lens can be inserted and removed from the cell, to a stable inspection position in which the inspection window is aligned with the optical axis of the and back again. For optical inspection of the contact lens, the one-piece cell first is filled with a liquid, usually water, in a filling station. To perform the filling action, the cell is arranged in its handling position, with an axis of the handling channel extending about parallel to the optical axis. Subsequently, the cell is loaded with the contact lens to be inspected at a lens loading station through the handling channel. Thereafter, the one-piece cell is tilted to its inspection position and transported to an inspection station. After the contact lens has been optically inspected, the cell is transported away from the inspection station, whereupon the cell is tilted back again to its handling position. In this handling position, the contact lens is removed from the one-piece cell, the liquid is removed from the cell, and the cell is transported back again to the filling station. The above-described cycle can then start anew.
Once the contact lens is inserted into the liquid contained in the one-piece cell and is allowed to settle down, a certain time period elapses until the lens has settled down to its rest position at the bottom of the cell. As the one-piece cell is tilted from the loading position into the inspection position, the liquid inside the cell is agitated. This results in the contact lens leaving its rest position again and floating in the liquid. Thus, before the lens can be optically inspected it must be allowed to settle down to its rest position again. The time period that elapses until the contact lens has settled down to its rest position at the bottom of the cell is generally comparable to the time period for the initial settling down after the loading of the contact lens. When the one-piece cell is tilted back to its loading position after the optical inspection of the contact lens, the liquid inside the cell is agitated again and, as a result, the lens floats in the liquid again. Before the lens can be removed from the cell, for example with the aid of a suction gripper which is inserted through the handling channel of the cell, it must again be waited until the lens has settled down to its rest position at the bottom of the cell. The time period that elapses each time until the contact lens floating in the liquid inside the cell has settled down into its rest position at the bottom of the cell may, for example, amount from about fifteen seconds to about twenty-five seconds, in order to be sure that the lens has completely settled down. During this time period neither an optical inspection of the contact lens can be performed, nor can the contact lens be removed from the cell. It is evident that such ‘waiting’ periods are inefficient in an automated contact lens production process. Accordingly, one object of the invention is to avoid such ‘waiting’ periods in order to further increase the efficiency of the production process.
When the contact lens is optically inspected the optical inspection system may also obtain positional information about the contact lens which is in its rest position at the bottom of the one-piece cell. Such positional information may, for example, be used for the positional control of a suction gripper or similar device used for the removal of the contact lens from the cell. However, in the afore-described case where the one-piece cell is tilted after inspection and, accordingly, the contact lens leaves its rest position and settles down again to a new rest position, such positional information is not accurate, because the contact lens usually will not settle down at the identical rest position at the bottom of the cell. Accordingly, another object of the invention is to be able to make use of contact lens positional information which has been obtained during optical inspection of the contact lens in order to improve the accuracy of the lens gripping process.